Most people understand that a frog never becomes an elephant. A frog is a frog. Then again, a tadpole is a tadpole. But is a tadpole a frog? Some folks would argue not: The tadpole has no lungs; it has gills. It has no legs; it has a tail. It looks and acts just like a fish. It can’t be a frog, can it? Well, it depends upon how you define the frog organism.
May we identify an organism as a frog purely on the basis of its morphology (physical form)? The biologist will say no. Three criteria are necessary for biological identification and morphology is only one of them. Physiology and genomics are the other two.
The biologist will not hesitate to affirm that the tadpole is, indeed, a frog. The living organism we call “frog” (Rana catabiensis) undergoes profound morphological and physiological changes in the course of its lifecycle. Although these changes are radical, the genetic code - the DNA blueprint that defines this particular organism - never changes.
The biologist will tell you that a frog is a frog from the instant it first functions as an independent organism, regardless of the form it takes during the course of its development. It will be nothing other than a frog when it dies. An organism is never identified purely on the basis of its morphological or physiological state at any given point in its lifecycle. It would be like declaring the benchmark of life for the butterfly organism is the presence of wings and antennae and then, after examining the caterpillar, pronouncing that, because it has neither wings nor antennae, it is neither living nor a butterfly, despite the fact that it is a living organism with the genome of the butterfly and, if it is not killed before it completes its metamorphosis, will become nothing other than a butterfly.
The same thing applies to the unborn. He may not have a face. Or limbs. Or a developed brain. Or any features of a born human being.He is still a human being, biologically speaking.